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Date: Fri, 10 Feb 2006 16:38:48 +0100
From: jerome lacoste <jerome.lacoste@gmail.com>
To: Joerg Schilling <schilling@fokus.fraunhofer.de>
Subject: Re: CD writing in future Linux (stirring up a hornets' nest)
Cc: dhazelton@enter.net, peter.read@gmail.com, mj@ucw.cz,
       matthias.andree@gmx.de, linux-kernel@vger.kernel.org,
       jim@why.dont.jablowme.net, jengelh@linux01.gwdg.de
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On 2/10/06, Joerg Schilling <schilling@fokus.fraunhofer.de> wrote:
> "D. Hazelton" <dhazelton@enter.net> wrote:
>
> > And does cdrecord even need libscg anymore? From having actually gone through
> > your code, Joerg, I can tell you that it does serve a larger purpose. But at
> > this point I have to ask - besides cdrecord and a few other _COMPACT_ _DISC_
> > writing programs, does _ANYONE_ use libscg? Is it ever used to access any
> > other devices that are either SCSI or use a SCSI command protocol (like
> > ATAPI)?  My point there is that you have a wonderful library, but despite
> > your wishes, there is no proof that it is ever used for anything except
> > writing/ripping CD's.
>
> Name a single program (not using libscg) that implements user space SCSI and runs
> on as many platforms as cdrecord/libscg does.


I have 2 technical questions, and I hope that you will take the time
to answer them.

1) extract from the README of the latest stable cdrtools package:

        Linux driver design oddities ******************************************
        Although cdrecord supports to use dev=/dev/sgc, it is not recommended
        and it is unsupported.

        The /dev/sg* device mapping in Linux is not stable! Using dev=/dev/sgc
        in a shell script may fail after a reboot because the device you want
        to talk to has moved to /dev/sgd. For the proper and OS independent
        dev=<bus>,<tgt>,<lun> syntax read the man page of cdrecord.

My understanding of that is you say to not use dev=/dev/sgc because it
isn't stable. Now that you've said that bus,tgt,lun is not stable on
Linux (because of a "Linux bug") why is the b,t,l scheme preferred
over the /dev/sg* one ?


2) design question:

- cdrecord scans then maps the device to the b,t,l scheme.
- the libsg uses the b,t,l ids in its interface to perform the operations

So now, if cdrecord could have a new option called -scanbusmap that
displays the mapping it performs in a way that people can parse the
output, I think that will solve most issues.

cdrecord already has this information available, it just doesn't display it:

$ cdrecord debug=2 dev=ATAPI -scanbus 2>&1 | grep INFO
INFO: /dev/hdc, (host0/bus1/target0/lun0) will be mapped on the
schilly bus No 0 (0,0,0)
INFO: /dev/hdd, (host0/bus1/target1/lun0) will be mapped on the
schilly bus No 0 (0,1,0)

It could perform in the following way:

$ cdrecord dev=ATAPI  -scanbusmap
...

0,0,0 <= /dev/hdc
0,1,0 <= /dev/hdd


Are you accepting such a patch?

Jerome
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